The production of images that convey the perception of depth to a human observer has traditionally been accomplished by analog photographic methods, such as integral and lenticular photography, which, while having a long history of theoretical consideration and demonstration, have enjoyed only limited commercial success. For examples of published material on the subject attention may be directed to a text by Takanori Okoshi, entitled "Three-Dimensional Imaging Techniques," Academic Press, New York, 1976; and an article by G. Lippman, entitled "E`preuves re`versibles, Photographics integrales," published in Comptes Rendus, pp. 146, 446-451, Mar. 2, 1908.
Integral photography refers to the composition of the overall image as an integration of a large number of microscopically small photographic image components. Each photographic image component is viewed through a separate small lens, usually formed as part of a mosaic of identical spherically-curved surfaces, that are embossed or otherwise formed onto the front surface of a sheet of translucent material (e.g. clear plastic) of appropriate thickness. This sheet is subsequently bonded or held in close contact with an emulsion layer containing the photographic image components.
Lenticular photography may be considered as a special case of integral photography, where the individual small lenses are formed as sections of cylinders running the full extent of the print area in the vertical direction. One recently commercialized attempt at a form of lenticular photography is the `Nimslo` camera, manufactured by a Hong Kong camera works and sold as a Nishika camera. Although a sense of depth is clearly visible, the resulting printed images have only limited depth realism, and appear to `jump` as the print image is `rocked` or the viewer's vantage relative to the image print is changed.
An analog optical technique of producing lenticular photographs, described in the above-referenced Okoshi text, involves affixing a photographic camera to a carriage on a slide rail, which allows the camera to be translated in a horizontal direction normal to the direction of the desired scene. Then, as the camera carriage is translated along the slide rail, respective photographic images are captured in successively equal increments, from a central vantage point to lateral vantage points on either side of the central vantage point. The distance that the lateral vantage points are spatially displaced from the central vantage point is dependent on the maximum angle at which the lenticular material can project photographic image components contained behind any given lenticule before it begins to project photographic image components contained behind an adjacent lenticule.
Although not necessary, the number of captured images may include a picture from the central vantage point, in which case the number of captured images will be odd. (If a picture from the central vantage point is included, the number of images will be odd.) The sum of the total number of views contained between and including the lateral vantage points will determine the number of photographic components which eventually will be contained behind each lenticule.
Negatives resulting from each of these views are then placed in an image enlarger which is equipped with a lens of the same focal length as the camera lens. Since the camera was moved laterally between successive exposures, as previously described, the positions of the images in the original scene will be seen to translate laterally across the film format. Consequently, the positions of the enlarged images from the negatives also move laterally with respect to the center of the enlarger's easel, as successive negatives are placed in the film gate.
An assemblage, consisting of a sheet of photographic material oriented with its emulsion in contact with the flat back side of a clear plastic sheet of appropriate thickness having lenticules embossed or otherwise formed into its other side, is then placed on the enlarger easel with the lenticular side facing the enlarger lens. The position of this sheet on the easel is adjusted until the field of the central image is centered on the center of the assemblage, and an exposure of the information being projected out of the enlarger lens is made through the lenticules onto the photographic emulsion. Thereafter, negatives from the successive exposures are placed in the film gate and the position of the assemblage is readjusted on the easel, so as to reposition each respective view to the center of the assemblage, and additional exposures of the information being projected from the enlarger lens are made.
When all the views between the lateral vantages have been similarly exposed on the emulsion through the lenticular plastic sheet, the film sheet can be separated from the lenticular plastic sheet and developed. If the aperture diameter of the enlarger lens is set at a value corresponding to the amount of lateral shift between alternate views, then the space behind each lenticule will be found to be exactly filled with photographic image components.
The final step in this process is to reassemble the photographic film and the plastic sheet again with intimate contact between the emulsion layer and the flat side of the lenticular plastics sheet and positioned laterally, so that the long strips of adjacent images resulting from exposures through the cylindrical lenticules are again positioned in a similar manner under the lenticules for viewing.
Ideally, an integral or lenticular photograph should display an infinite number of different angular views from each lenslet or lenticule. From a practical standpoint, however, this is not possible since each angular view must have a corresponding small finite area of exposed emulsion or other hard copy media. As a consequence, as an upper limit, the number of views must not exceed the resolution limit of the hard copy media.
In a print obtained by the above-referenced `Nimslo` camera, the number of views behind each lens is limited to four views, two of which are considered left perspective views and the remaining two are considered as right perspective views. This is well below the resolution limit of conventional photographic emulsions and allows for only two options of stereoscopic viewing perspective as the viewer's head moves laterally.
Optical multiple projection has also been utilized in experiments by Eastman Kodak to produce a print by means of a large number of cameras taking alternate views of the scene to provide a smooth transition of perspectives for each lens. This method of image recording is called `indirect multiple optical projection and recording` since the final print recording is derived `indirectly` from a series of two-dimensional image recordings.
The concept of integral photography by indirect optical recording is also described in the U.S. Patents to Wright, Nos. 4,724,449 (or the '449 patent) and 4,956,705 (or the '705 patent). The '449 Patent describes a photographic camera with a laterally shifting film holder essentially similar to the techniques described by Okoshi to capture a number of perspectives of a scene and recording image information onto different negatives for eventual processing into three-dimensional prints. Although the manner in which a viewable print is obtained from the negatives is not described, it may be inferred that image separation must be provided only in the horizontal direction, since only lateral camera motion is described. This suggests that either the lenticular means described above is used, or raster occlusion, such as using a Ronchi ruling on a faceplate spatially located in front of the composite print so as to prevent the images intended for viewing by the right eye to be seen by the left eye and vice versa, is the mode of print display. A technique of raster occlusion to produce a print has been described extensively in textbooks (see, for example, the texts by L Lipton, "Foundations of the Stereoscopic Camera," Van Nostrand Reinhold, New York, 1978; and by N. A. Valyus, "Stereoscopy," Focal Press, London, 1962) and suffers from the additional problem of reduced image brightness.
The above-referenced '705 Patent describes the same image capture process using video charge coupled device (CCD) array cameras, rather than photographic cameras, and further discusses capturing the images using a "frame. grabber" board in a computer which "freezes a frame of a still or moving object and digitizes the image for further processing."
Prior to the development of `direct` printing processes, such as described in the U.S. Pat. Nos. 4,552,853 and 4,674,853. techniques for optically recording scenes on lenticular print material, so that the angular presentations of the lenslets corresponded correctly with the angular orientations of the original scene, relied upon indirect printing process.
A `direct` printing process involves recording images using correct angular correlation. According to this method, a converging bundle of optical rays from a very large aperture camera lens is directed onto a sheet of lenticular material to which photographic film has been affixed in the same manner employed in the projection method, described previously.